Styrene is a basic building block for the manufacture of a broad range of materials. It is used to make polystyrene, acrylonitrile-butadiene-styrene, polyester resins, synthetic rubber, and a host of other products.
Production of styrene by dehydrogenation of ethylbenzene is commonly conducted by mixing ethylbenzene with steam and passing the mixture through a dehydrogenation catalyst-packed bed. Steam is used as the diluent gas in the dehydrogenation reaction system to supply heat needed for the endothermic reaction of ethylbenzene to styrene. Steam/water is also used to lower the boiling point of the ethylbenzene feed, either at the azeotropic composition (i.e. minimum boiling point) or at some non-azeotropic composition (i.e. reduced boiling point). See U.S. Pat. Nos. 4,628,136 and 4,765,398, each incorporated herein in the entirety. The vaporized ethylbenzene/steam is mixed with the diluent steam/water before feeding the dehydrogenation reactors, so the water contained therein is complementary to the dilution stream required in the reaction system.
Lowering the boiling point of ethylbenzene allows the use of low level heat to vaporize the ethylbenzene feed to the dehydrogenation reaction system. Despite the use of steam/water to lower the boiling point of ethylbenzene feed, the use of steam reduces the overall energy efficiency of the process. As an alternative, Samsung Total Petrochemicals Co. (Korean Patent Pub. No. 20060092305) used inert gas in place of all or part of the steam to reduce the boiling point of the ethylbenzene feed. However, the addition of inerts to the reactor feed adds to the raw material requirements of the process and the offgas compressor load and power requirements. The inert gas may also not be entirely inert, and may detrimentally affect the equilibrium reaction of ethylbenzene dehydrogenation or the catalyst activity.
A process that economically lowers the boiling point of the ethylbenzene feed in an oxidative ethylbenzene dehydrogenation process has not been reported. As such, there exists an ongoing and unmet need in the industry for economical and energy efficient methods for styrene monomer production from ethylbenzene feedstocks.